Marianna Balasco

1/fα Fluctuations in geoelectrical signals observed in a seismic area of Southern Italy

Abstract Recent studies have shown that many natural systems display temporal fluctuations with long-range power-law correlations, suggesting a fractal geometry of the underlying dynamical system. Four geoelectrical time series, measured in a seismic area of Southern Italy, are investigated by means of spectral tools in order to evidence the existence of power-law correlations. Results show the scaling behaviour for all the signals recorded, pointing to the presence of fractal features expressing a long-term correlation with scaling exponents which indicate stabilizing mechanisms. Furthermore, our findings suggest an observational evidence of correlations between the variation of parameters describing the temporal fluctuations of geoelectrical signals and earthquakes that occurred in the area investigated.

Design of a new prototype of remote station to detect electrical and seismometric parameters in a seismic area of Southern Italy

Abstract In this work we describe the main features of a new prototype of remote station able to jointly detect electrical and seismometric parameters. The measuring station has been installed at Tito site on the Southern Apennine chain, one of the most seismic active areas of the Mediterranean region; it combines new technologies for the data acquisition with a robust statistical technique to discriminate anomalous fluctuations from background noise in the recorded signals. The completely automatic station is equipped with sensors able to detect self-potential signals (16 channels, A/D 24 bit, sampling rate of 0.25Hz) and a 1Hz three directional seismometer connected to an acquisition unit having a dynamics of 133 dB. After a preliminary filtering procedure, mainly devoted to remove all the influences due to meteo-climatic parameters and/or cultural electrical noise, a software developed ad hoc to study the possible correlation between anomalous patterns in electrical signals and local microseismic activity was employed. In particular, the instrumental features of the new station allow us to compare the fluctuations of electrical signal, detected at short temporal scales, with seismic events with low magnitude (M

Dynamics of internal and external origin revealed by a single-site magnetotelluric monitoring

A continuously operating magnetotelluric (MT) system was installed in Agri Valley (Southern Italy) by the Institute of Methodologies for the Environmental Analysis (IMAA) for studying the temporal stability of the electric properties of the subsoil. In a previous work, Balasco et al. (2008) analysed 1-year-long dataset evidencing possible source effects. Such effects are deeply investigated in this work considering almost three years monitoring. Two different types of dynamics are revealed: i) a seasonal fluctuation at short sounding periods, and ii) a behaviour linked to the external geomagnetic activity index at high periods.

QUANTIFYING PERSISTENT BEHAVIOR IN EARTH'S APPARENT RESISTIVITY TIME SERIES

The multiple segmenting method (MSM) has been applied to investigate the scaling behaviour in the Earths apparent resistivity time series, measured in a seismic area of southern Italy. The study of apparent resistivity represents one of the most important scientific challenges in the studies devoted to the geophysical monitoring. Our results show that apparent resistivity is characterized by a persistent scaling behaviour at all the periods considered, with the scaling exponent tending approximately to 0.5.

A New Prototype of a Remote Station for the Monitoring of Geoelectrical Parameters in Seismic Active Areas

We describe a new prototype of a remote station for the continuous measuring of geoelectrical parameters in seismic active areas. The design of the monitoring equipment combines advanced technologies for electrical sensors with robust statistical methodologies for the identification of anomalous patterns in the recorded signals, possibly related to local seismic events. The main features of the remote station have been highlighted analyzing the data measured in a seismic active area of Southern Apennine chain (Italy). An acquisition unit operating with a 24 bit A/D converter controls a multi-electrode array equipped with sensors able to detect the temporal fluctuations of electrical field on the earth surface. In a first step, we have developed a software package able to check those factors that can contaminate the electrical parameters, such as the rainfall events. In a second step, we investigated the inner dynamical structure of the measured data at different time scales; then, it has been verified that the temporal fluctuations of the electrical signals are well described by a first-order autoregressive process.Taking into account the quantitative dynamics extracted by the geoelectrical time series, we began to study the so-called extreme events (or runs), i.e., that consecutive values above/below a fixed threshold with a low occurrence probability. Finally, we attempted to identify such events and to study their correlation with the seismic phenomena observed in the investigated area.

FRACTAL ANALYSIS OF THE HOURLY TIME VARIABILITY IN SELF-POTENTIAL AND FLOW VARIATIONS CONCOMITANTLY MEASURED IN THE SOOS NATURE PARK (CZECH REPUBLIC)

Scaling properties of self-potential and carbon dioxide flow rate data, concomitantly recorded in a CO2 degassing area at Soos, Bohemia (Czech Republic), have been investigated by means of several fractal tools. The power spectra, behaving as power law function of the frequency, show the presence of colored noise-type dynamics. The Higuchi analysis reveals the self-potential and flow signals to have the property of fractal curves. The variograms, analyzing time-scales stretching from one hour to almost 50 hours, reveal the presence of approximately three time-scaling ranges, characterized by different features in terms of persistence of the processes underlying the signals.